Phase Aligned Time-Reversal for Multi-User Wireless Power Transfer Systems With Non-Linear Energy Harvesting

Abstract

In this paper, we study a waveform design based on time-reversal (TR) for multi-user wireless power transfer (WPT) systems in multipath channels. The existing waveforms for WPT using the nonlinear energy harvesting (EH) model have been designed in the frequency domain, whereas we design the waveform directly in the time domain by modifying TR to be suitable for WPT. In the non-linear EH model, the peak signal with the largest magnitude among the received signals is responsible for most of the harvested energy at the energy receiver (ER). Since the peak signal of TR for multi-user consists of the sum of the inter-user interference (IUI) signals and the desired signal, the phase difference between these signals can reduce the magnitude of the peak signal. Thus, we propose a novel waveform based on TR, called a phase aligned TR (PATR). The objective of the proposed PATR is to increase the harvested energy by aligning the phase between the IUI signal and desired signal as in-phase. We derive the optimal phase set to be pre-rotated for maximizing the peak signal, and design the PATR waveform by combining the modified TR and the derived optimal phase set. We prove the superior performance of the proposed PATR compared to the existing schemes in the multi-user WPT systems with the non-linear EH model by simulation. Moreover, we show that the gain for the harvested energy of the proposed PATR increases as the number of transmit antennas and the number of ERs increase.INDEX TERMS Wireless power transfer, energy harvesting, time-reversal, non-linear energy harvesting circuit, interference alignment.

Receiver Architecture Design and Analysis for NOMA-Based Multi-User Communication Systems

“…From the perspective of energy harvesting, TR enhances the capabilities of wirelessly powered devices by making full use of the multipath propagation to sustain the received power at the harvester input [4]. This is different from conventional harvesting techniques where the power density of the wireless signal received by the antenna is affected by multiple factors including multipath channels, shadowing effects, and largescale path loss.…”

Influence of Time‐Varying Atmospheric Channel on Time Reversal Spatial Power Combination of Sparse Array on Ground

“…So the TR technique can adaptively compensate for the phase generated by the channel and focus signals. Since the TR technique was introduced into electromagnetics (Lerosey et al., 2004), it has been widely used in the fields of super‐resolution focusing (Ding et al., 2013; Ge et al., 2011; Lerosey et al., 2007), high‐precision positioning (Li, Liu, Zhao, & Hu, 2019; Liang, 2020; Zhou et al., 2014, 2015), wireless power transmission (An et al., 2021; Ku et al., 2016; Li, Liu, Zhang, et al., 2019; Liu et al., 2011; Park & Hong, 2020, 2021; Y. Wang et al., 2021; Yang et al., 2021; Zhao, Yue, et al., 2012), spatial power combination (Q. Chen et al., 2015; Tian, 2019; Z. Wang et al., 2019; Zhong & Liao, 2016), and so on. In addition, Wang's team has also carried out a series of research on TR technology in shaping electromagnetic fields (Z. Chen et al., 2021; Li, Zhao, et al., 2019), wireless communication (Jin et al., 2013; Z. Wang et al., 2019; Zhao et al., 2014), beam‐steering (Zhao, Jin, et al., 2012), and other fields.…”